Reusable reaction vessel



Feb 26, 1963 T. s. soma 3,079,136

REUSABLE REACTION VESSEL Filed April 26. 1961 INVENTOR. )jy/ef' 5. SomeBY /fw Qld-m ffZar//gy United States Patent Otice 3,079,136 PatentedFel). 26, 1963 3,379,136 REUSABIJE REACTHN ESSEL Tyler S. Soins,Richland, Wash., assigner to the United States of America as representedhy the United States Atomic Energy Commission Filed Apr. 26, 1961, Ser.No. @5,526 Claims. (tCl. 2456-39) The invention relates to a novelvessel for high temperature chemical reactions capable of being reused,and to a method of making the same, more particularly, to such a vesselfor use in reductions of the compounds of heavy metals such as theactinides, by reducing metals such as calcium, magnesium, and sodium.

Surprising as the statement may seem, no reaction Vessel has previouslybeen developed for reactions of the kind mentioned, which can be reused.The severe stresses, mechanical and thermal, from such reactions causebreakage in virtually every case in spite of the fact that the vesselsare made of most refractory materials available, such as magnesia. Thebreakage is, of itself, expensive, but more important is the hazard andexpense of the cleanup which it occasions; since actinide fuels are bothhazardous and economically valuable all traces that escape from thevessel, as well as those adhering to its sides, must be removed andrecovered. If a reusable vessel could be provided it would thereforeresult in both increased safety and economy on two scores, one in thatthe number of vessels required would be reduced, and secondly in thatthe cleanups would be eliminated between batches. Fresh charges could beintroduced without removing the residues from previous charges, and athoroughgoing removal would be necessary only once in the life of eachvessel, when its period of usefulness had come to an end.

Numerous attempts have been made, as might be expected, to improve thesituation. One of these has been to surround the refractory vessel, orCrucible, with a metal shell of somewhat greater inside dimensions thanthose of the outside of the Crucible, and lilling the space between thetwo with loose refractory material, preferably the same material as thematerial from which the crucible was made. This gives the Cruciblesupport during the chemical reaction; it may possibly delay its breakageuntil the reaction runs its course somewhat more completely, and whenthe inevitable breaking occurs it limits the spread of the contents ofthe crucible. Nevertheless, this does not make for a reusable vessel,with the desired advantages .above outlined.

It is, accordingly, an object of the invention to provide a reusablereaction vessel capable of withstanding the resses of repeated hightemperature chemical reactions.

It is a further object to provide such a reusable reaction vessel forreductions of the compounds of heavy metals such as the oxides and saltsof the actinides, by reducing metals such as calcium, magnesium andsodium.

It is a further object to provide a method of making vessels of the kindset forth in the foregoing object paragraphs.

All the foregoing objects are attained by my discovery that a refractoryvessel surrounded by a metal shell and loose refractory material in thespace between the vessel and the shell can be made reusable byimpregnating in a certain manner the vessel and the refractory materialwith a salt or a mixture of salts which fuse at a higher temperaturethan the initiating temperature of the chemical reaction to be carriedout in the vessel but below the melting points of the other materials ofconstruction. Sintered magnesia crucibles surrounded by metal shells andwith beds of loose magnesia therebetween, for example, treated withimpregnating salts according to the invention, can be used for anaverage of 12 batches with a breakage rate of virtually zero; smallsized crucibles of the same kind have lasted on the average from 18 to20 batches.

It is essential that both the vessel and its surrounding bed bethoroughly impregnated with the fusible salt so as to make a firmunitary structure capable of withstanding the thermal shock of thereaction. In reductions of the kind above described this shock takesplace soon after the initiating temperature is reached; when plutoniumtrichloride is reduced by calcium, for example, the initiatingtemperature is about 280 and the thermal shock takes place below themelting point of the impregnating salt. For this reason the impregnationmust be carried out in such a way that the structure be rm, and I havefound that this requisite firmness can be secured by melting thenecessary quantity of impregnating salt within the crucible and thentilting and rotating it until all the salt percolates out through theshell of the crucible through its pores. Merely mixing the sand bed andsalt together in the dry state and then heating them does not suflice;v

this neither impregnates the pores of the Crucible, nor does it producethe iirm structure needed within the surrounding bed.

The impregnating salt should be solid at the initiating temperature ofthe reaction, and preferably at the highest temperature of the exteriorof the crucible during the entire reaction as well.

Reference is now made tothe FIGURE which is a sectional view of atypical embodiment of the invention. 2 is a cylindrical Crucible ofconventional shape and construction of refractory material made coherentby some such process as sintering. Crucible 2 is preferably of magnesiasintered together so as to make the somewhat porous structure which iscustomary in crucibles of this general type. 3 is a surrounding metalshell, preferably of stainless steel, of cylindrical shape, with insidedimensions somewhat greater than the outside dimensions of the Crucible2. 4 is ka compacted bed of uncohered refractory material, againpreferably magnesia, which occupies substantially all the space betweenthe crucible 2 and the shell 3. Both crucible 2, throughout its pores,and compacted bed 4 are impregnated with a salt or salt mixture,

as will now be explained.

In carrying out the invention, any salt or salt mixture may be usedwhich is thermally conductive in the solid state and which melts at atemperature above the initiating temperature of the reaction to becarried out and below the melting point of the other structuralmaterials. Halides of the alkali and alkaline earth metals meet theserequirements. In certain instances, it is preferable to select a saltwhich is also one of the reaction products since this simplies theproblem of separation by limiting the number of chemical individuals tobe dealt with. On the other hand, such a selection can in certaininstances have adverse eiiects, such as causing unwanted precipitationby exceeding the solubility product, shifting the equilibrium of thereaction in an undesired direction and the like; such adverse effectsmay be sufficiently important in some cases that the advantages oflimiting the number of chemical individuals become outweighed. The useof mixtures, particularly eutectic mixtures, has the advantage oflowering the melting point of the salt component, and this again, mayoutweigh the advantage of simplicity inherent in a pure salt.

Since calcium, magnesium, and sodium are the most commonly used reducingmetals, the halides of these metals are preferable in the great majorityof instances, examples being CaCl2, CaF2, NaCl, NaF, and mixturesthereof. A mixture of 8O mole percent NaF with 20 mole percent CaF2 hasgiven good results.

The salt or salt mixtures having been selected to meet theyrecnlirernents of the particular reaction, the quantity steil should besniiicient to impregnato the riores of the crucible and the surroundingbed of loose refractory rnaterial Without any excess.

.Y Example A hollow. right. cylindervof .stanlesssteel open at one endhad walls about 1/56 inch thick and measured 10 inches. nigh and 3,1/2inches in outside diameter. Into thisv placed a crnoible. of roughly thesaine shone Inode of sintered porous magnesio rneasuring about. Slots inhes higli `and with an outer diameter of about 31/4 inches. :Forconvenience, themonth of the .crucible was closed with a rubber stopperand about 400 grains of magnesio sends-wete poured around it inside thestainless steel cylinder until the sixteenth of an inch .spaceseperating tbe two was completely tilled by tbe sand.

Ttiefstonper was then removed and about 3,00. grains of clciunlcnioriderete placed in the cruciblelne assent: bly` then placed in a beatingfurnace having e remotely controlled; manipulator, and heated to 900 C-ATfb @nin letton tilted entlfturned .tbe assembly as tbe lien. e.continued nntilcll. the .calcium chloride lett-thc.` insiste et,crucible thereby ininresncting it and the niagneslie, sentit` Thenseetnblyanow a 4nnitcry reaction vesselsivss Withdrawn troni tbebeating furnace ,and Perinittedrto cool- In atypical use, tbc vessel wascharged with 700 grams of plutonium trichloride and the stoichiornetr-icamount of metallic calciunirequired for itsreduction and plaeedin areaction funraee upon a bed of loose magnesia :sand Y in a rectangularcontainer. After the reaction was complete the vessel was remoyed fromthe reaction furnace and permitted to cool. Theplutonum Inetalfwes foundto here congealcd inv a button shape whichwas recovered by drillingl theslag until the metal button becsnie' loose; and inverting the vessel"l'heviressel was're'chargd Awithout further decontarnination enti' theprocess, ieiiented 'eleven incre linien? Dine j p 1 ne .showed ne er butet' Vthe enel"-tl1e,insiiic Vbottom"nresente`da deteriorated aipearancethat it v'v'as deemed Y, i l` S'theYs lll" i Y Allltbe foreg .ngonerations tf1-ere carried out in airtigirr grovehoreseimnted from theenvironment.'

hat this invention is not to be li A Y t A Y i1, herein, but that it maybe modified 'Within tbescone of the. 'entienden ,cInirns-Y ANhtisClaimed is: A

l., A reusable reaction Vesselconlprising an outer metal CTI shell, aninner container of porous coherent refractory material., andtherebetween a bed ot uncohered refractory.

material, said inner container and said bed both being impregnated by aninorganic salt which is thermally conductive in the solid state 4andwhich melts below the melting point of the construction rnaterials ofthe vessel.

2. The vessel of claim l where the inorganic salt is a salt mixture.

3. The vessel of claim 1 Where the container of porous coherentrefractory material is sintered magnesia, the refractory material ismagnesia sand and the inorganic salt is selected from the groupconsisting of alkali metal halides and alkaline earth metal halides.

4. A method `of making a reusable reaction vessel comprising placing aninner container of coherent refractory material within a surroundingmetal shell of slightly greater inside dimensions than the outsidedimensions of the container, filling the space therebetween withnncohered'refractoryv material, and impregnating both the innercontainer and the uncohered refractory material with an .inorganic saltwhich is thermally conductive in the solid state and which melts belowthe melting point ofthe, other parts of the yessel and above theinitiating temnerntnre of the reaction to be carried out in the vessel.

5e A; method of melting a reusable reaction vessel for` stiuctonmateriel of the reaction vessel and, higher than,`

tbe initiating temperature of. the said reduction, raising tbe. ambient,temperature tornelt. seid inorganic salt; tilt.- ing and rotating thereaction vessel until the entire quan; my ot inorganic salt nercclatesthrough the walls ct the inner container and said inner containerandnsaid inag-V Iiecin. Sand are. both thoeonslily impregnated therewithReferences Cited in the fiile of this patent UNITED STATES PATENTS

1. A REUSABLE REACTION VESSEL COMPRISING AN OUTER METAL SHELL, AN INNERCONTAINER OF POROUS COHERENT REFRACTORY MATERIAL, AND THEREBETWEEN A BEDOF UNCOHERED REFRACTORY MATERIAL, SAID INNER CONTAINER AND SAID BED BOTHBEING